The present invention relates to screen printing, and in particular to a novel printing screen, kit and method for accurately printing curved surfaces.
Screen printers for articles having arcuately shaped surfaces, such as food containers, barrels, drinking glasses, bottles, hats, and the like, are well known, and generally include a curved printing screen which mates with the rounded configuration of the object to be printed.
Heretofore, it has been extremely difficult and expensive to fabricate such a curved printing screen without distorting the pattern. For instance, one method for fabricating arcuate printing screens is illustrated in U.S. Pat. No. 2,347,022, and comprises forming the pattern on a flat sheet of screen fabric, and then adhering the screen to a flexible frame. However, when the frame is bent into the desired configuration, the screen is tensed unevenly, and tends to bow or cup at the center. This non-uniform stretching distorts the printing pattern from its true shape, so that the images printed are not properly proportioned. Further, the bowed printing screen prevents the screen from abutting flat against the article, and thereby causes smearing so that the images printed are not clean and clear. The inaccuracies inherent in such printing screens are particularly pronounced in multi-colored printing, as it is virtually impossible to properly register the distorted patterns. Also, if a flat squeegee is used on such screens, the ink is not uniformly applied to the article.
Another screen assembly method designed to overcome such difficulties, comprises mounting a panel of screen fabric in a pre-formed, arcuately shaped frame which fits the curved article. The screen fabric is treated for photosensitivity, and a film positive is taped to the front side of the screen. The screen is positioned on a clear plastic or glass mandrel having the same contour as the screen, and is held in place by clamps or weights. Ultraviolet light is beamed through the mandrel causing the screen to become exposed, and transferring the printing pattern thereonto. In such processes, the ultraviolet light is dispersed as it passes through the mandrel, thereby causing distortion in the transferred printing pattern. Further, this method is quite expensive, complex, and requires sophisticated equipment, so that it is not adapted to make screens for specialty, low volume printing applications, such as hats, or the like. Since specialty screen printing in small shops and stands has become very popular as of late, there is an increasing demand for a high quality, arcuate printing screen which can be fabricated quickly, easily, and inexpensively.
Yet another method for fabricating screens to print arcuate objects comprises forming the printing pattern on a flat panel of screen fabric, and then hand stretching the screen onto a pre-formed, curved frame. Although this technique is rather simple, the screen material cannot be uniformly tensed by hand, thereby causing distortion in the printing pattern. Also, it is virtually impossible to mount mating portions of a multi-color design in a manner that will assure proper registry.